MOLECULAR CHARACTERISATION OF HEPATITIS B VIRUS VACCINE ESCAPE MUTANTS IN SOUTH AFRICA

Transcription

1 MOLECULAR CHARACTERISATION OF HEPATITIS B VIRUS VACCINE ESCAPE MUTANTS IN SOUTH AFRICA Penny Crowther Dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Medicine Johannesburg, 2005

2 DECLARATION I, Penny Crowther, declare that this dissertation is my own work. It is being submitted for the degree of Master of Science in Medicine at the University of the Witwatersrand, Johannesburg. It has not been submitted before for any degree or examination at this or any other University... day of ii

3 ABSTRACT Since the introduction of vaccination against hepatitis B virus (HBV) infection in South Africa, at least one case of infection despite vaccination has occurred. The purpose of this study was to determine whether this infection was the result of mutations within the region of the surface (S) gene encoding the a determinant epitopes of the hepatitis B surface antigen, which permitted viral vaccine-escape. HBV DNA was extracted from the serum and liver tissue of the patient and amplified within the complete bp genome and S gene, respectively. Following cloning, sequencing revealed a minor population displaying unique or uncommon S gene mutations that resulted in C138R, C139R, K141R, P142L, T143A, N146D, and T148A amino acid substitutions in the clones from the serum, and C139Y and D144N in the clones from the liver. Such isolates may represent South African HBV vaccine-escape mutants that caused chronic infection in the host prior to their reversion to wild-type. iii

4 ACKNOWLEDGEMENTS I would like to thank my supervisors, Dr Anna Kramvis and Professor Kew, for all their help and advice on this project, as well as for their endless support when it was needed most. To my parents, thank you for your encouragement and support during this degree, and for always being there for me. And to my friends in the Molecular Hepatology Research Unit, thank you for offering help and advice when it was needed, and for keeping me sane. I gratefully acknowledge the financial assistance provided to me by the University of the Witwatersrand, the National Research Foundation, and the Poliomyelitis Research Foundation. iv

5 TABLE OF CONTENTS DECLARATION... ii ABSTRACT... iii ACKNOWLEDGEMENTS... iv TABLE OF CONTENTS...v LIST OF FIGURES... viii LIST OF TABLES... ix ABBREVIATIONS...x Chapter 1: INTRODUCTION HEPATITIS B VIRUS History Natural History and Pathogenesis Epidemiology Classification Virion Structure Genomic Organisation and Gene Products Core Genes Polymerase Gene X Gene Surface Genes Replication Host Immune Responses Targeting HBV HBV Variants Genotypes Serological Subtypes HBV VACCINES Development Immune Response Implementation of Vaccination Vaccination Programme in South Africa SURFACE GENE MUTATIONS AND VACCINE ESCAPE RATIONALE AND AIMS OF THE STUDY...43 v

6 Chapter 2: MATERIALS AND METHODS SUBJECT AND SAMPLES DNA EXTRACTIONS DNA Extraction From Serum DNA Extraction From Liver Tissue AMPLIFICATION OF HBV DNA Full-Length Genome Amplification Surface Gene Amplification DETECTION OF AMPLIFIED DNA PRODUCTS CLONING OF AMPLIFIED DNA PRODUCTS Addition of 3 A Overhangs DNA Purification Cloning and Transformation Isolation of Recombinant Plasmid DNA GENOTYPING OF HBV DNA NUCLEOTIDE SEQUENCING OF HBV DNA SEQUENCING DATA AND PHYLOGENETIC ANALYSIS...66 Chapter 3: RESULTS DETECTION OF AMPLIFIED DNA PRODUCTS Full-Length Genome Amplicons Surface Gene Amplicons IDENTIFICATION OF HBV POSITIVE CLONES HBV GENOTYPING BY RFLP ANALYSIS Genotyping A to H Subgenotyping A1 versus A DNA SEQUENCING ANALYSIS Full-Length Genome Clones from Serum Surface Gene Clones from Serum Surface Gene Clones from Liver Tissue PHYLOGENETIC ANALYSIS...82 Chapter 4: DISCUSSION...84 Chapter 5: CONCLUSION...98 Chapter 6: REFERENCES...99 Appendix A: COMPLETE PATIENT INFORMATION vi

7 Appendix B: ETHICS APPROVAL AND PATIENT S INFORMED CONSENT.121 Appendix C: SOLUTIONS AND RECIPES vii

8 LIST OF FIGURES Figure 1.1 Schematic representation of the pathogenesis of hepatitis B virus infection in adults...5 Figure 1.2 World map showing geographic distribution of chronic HBV infection...8 Figure 1.3 Structure of HBV virions and subviral particles...12 Figure 1.4 Schematic representation of the HBV genome...14 Figure 1.5 Topological models of the three HBV surface proteins...21 Figure 1.6 HBV DNA synthesis by reverse transcription during replication...27 Figure 1.7 Diagrammatic representation of the major hydrophilic region of the HBsAg (aa ) occurring on the surface of the viral envelope...40 Figure 3.1 Detection of the amplified HBV full-length genome...67 Figure 3.2 Detection of the amplified HBV surface gene...68 Figure 3.3 Identification of full-length HBV positive clones...69 Figure 3.4 Identification of HBV surface gene positive clones...70 Figure 3.5 Restriction fragment length polymorphism (RFLP) analysis of the HBV surface gene (nt ) amplified from all of the serum and liver tissue clones...71 Figure 3.6 RFLP analysis of the HBV surface and polymerase gene (nt ) amplified from the serum full-length genome clones, showing the characteristic pattern of subgenotype A Figure 3.7 Chromatogram produced following automated sequencing of the core gene of the patient s HBV isolates...73 Figure 3.8 Amino acid sequence of part of the HBsAg (aa ), deduced from the nucleotide sequence of HBV S gene DNA (nt ) from the patient s serum- and liver-derived HBV clones...79 Figure 3.9 Schematic diagram of the HBsAg a determinant (aa ) showing single amino acid mutations found between aa 124 and Figure 3.10 Dendrogram obtained by neighbour-joining phylogenetic analysis of HBV complete genome sequences rooted on genotype F...83 viii

9 LIST OF TABLES Table 1.1 Relationship between HBV genotypes and subtypes, and corresponding characteristics...33 Table 1.2 Amino acid residues within HBsAg specifying the antigenic subtype determinants of HBV...34 Table 1.3 Common vaccine-escape mutations found between amino acids 124 and 147 within the a determinant of HBsAg...42 Table 2.1 Oligonucleotide primers used for the PCR amplification of the full-length HBV genome...49 Table 2.2 Oligonucleotide primers used for the PCR amplification of the surface gene of HBV...51 Table 2.3 Oligonucleotide primers used for the PCR amplification of parts of the S and P genes of HBV for A1 versus A2 genotyping...62 Table 2.4 Oligonucleotide primers used for sequencing the full-length genome and S gene of HBV...65 Table 3.1 Summary of mutations found within the region of the S gene encoding the MHR (aa ) of the HBsAg from HBV clones...81 Table A1 Patient information including ALT and AST levels, and HBV antigen and antibody status...98 ix

10 ABBREVIATIONS 3 A 3 deoxyadenosine aa ALT anti-hbc anti-hbe anti-hbs APC AST bp C cccdna ddntp DNA dntp DR dsdna EPI ER HBc HBcAg HBe HBeAg HBIg amino acid alanine aminotransferase hepatitis B core antibodies hepatitis B e antibodies hepatitis B surface antibodies antigen presenting cell aspartate aminotransferase base pair(s) core covalently closed circular deoxyribonucleic acid 2,3 -dideoxynucleoside triphosphate deoxyribonucleic acid deoxyribonucleotide triphosphate direct repeat double-stranded deoxyribonucleic acid Expanded Programme on Immunisation endoplasmic reticulum hepatitis B core hepatitis B core antigen hepatitis B e hepatitis B e antigen hepatitis B immunoglobulin x

11 HBs HBsAg HBV HBx HBxAg HCC kb kda LB MHC MHR mrna nt ORF P PCR pgrna PreC RFLP RNA RNase H rpm S V vol hepatitis B surface hepatitis B surface antigen hepatitis B virus hepatitis B x hepatitis B x antigen hepatocellular carcinoma kilobase(s) kilodalton(s) Luria-Bertani major histocompatibility complex major hydrophilic region messenger ribonucleic acid nucleotide(s) open reading frame polymerase polymerase chain reaction pregenomic ribonucleic acid precore restriction fragment length polymorphism ribonucleic acid ribonuclease H revolutions per minute surface volt(s) volume xi

12 Chapter 1: INTRODUCTION Hepatitis B, a serious liver disease induced by the hepatitis B virus (HBV), is a major global public health problem with the virus infecting over two billion people, of which approximately 387 million are chronically infected [World Health Organisation, 2002]. Since the development of hepatitis B vaccines, the number of newly acquired HBV infections has decreased substantially, to a very small fraction of the number acquired prior to vaccine administration. Nevertheless, vaccination does not protect all individuals from infection, because of either weak immune responses from the host or viral mutations, both of which allow vaccine escape of the virus. 1.1 HEPATITIS B VIRUS History Epidemic jaundice was first described by Hippocrates in the fifth century BC, when he was undoubtedly referring to individuals infected with hepatitis B virus and other agents capable of infecting the liver [Mahoney, 1999]. Epidemics of jaundice have continued to occur throughout history, particularly during wars in the 19 th and 20 th centuries [Mahoney, 1999]. The existence of a form of hepatitis that was parenterally transmitted by direct inoculation of blood or blood products was first documented by Lurman in Bremen, Germany, in 1883, 1

13 during a smallpox vaccination campaign that utilised contaminated human lymph [Lurman, 1885]. Early in the 20 th century, further outbreaks of parenterally acquired hepatitis occurred in various risk groups including patients who attended clinics for venereal diseases, diabetes, and tuberculosis; those who received blood transfusions; persons inoculated with mumps or measles serum; and military personnel who received yellow fever vaccines during World War II [Neefe et al., 1946; Mahoney, 1999]. Studies conducted during the 1930s and 1940s provided convincing evidence of a viral cause for hepatitis, with at least two etiologic agents [MacCallum and Bauer, 1944; Havens, 1946]. Subsequently, in 1947, MacCallum and Bauer (1947) proposed the nomenclature of hepatitis A for infectious hepatitis and hepatitis B for homologous serum hepatitis, terms which have since been adopted by the World Health Organisation (WHO) Committee on Viral Hepatitis. The distinctive seroepidemiologic features of hepatitis A and B were finally firmly established in a series of studies by Krugman and colleagues (1967) at the Willowbrook State School, New York, in the 1960s. The viral agent associated with hepatitis B was first isolated during serological studies conducted independently by Prince et al. (1964) and Blumberg et al. (1965). In searching for serum protein polymorphisms linked to diseases, Blumberg and colleagues identified an antigen termed Australia (Au) antigen in serum from patients with leukaemia, leprosy, and hepatitis, although the relationship of the antigen to hepatitis was not fully recognised until Prince (1968) subsequently established that the Au antigen occurred specifically in the serum of hepatitis B patients, and in 1973 the antigen was renamed the hepatitis B surface antigen (HBsAg) by the WHO. 2

14 In 1970, Dane and colleagues (1970) were the first to detect complete hepatitis B virions, or Dane particles. The 42 nm double-shelled spheres consisted of an outer envelope composed of HBsAg and an inner core containing hepatitis B core antigen (HBcAg) and endogenous DNA. A third antigen related to infectivity, designated hepatitis B e antigen (HBeAg), was subsequently described in 1972 by Magnius and Espmark (1972). In 1975, following these important breakthroughs in hepatitis research, hepatitis B vaccine studies were initiated using plasma-derived highly purified HBsAg particles, as it was found that antibodies targeting HBsAg were the neutralising antibodies for infectious HBV [Hollinger et al., 1974]. The safety and efficacy of these vaccines have since been established and continue to be maintained Natural History and Pathogenesis The hepatitis B virus is one of the most successful viral pathogens of humans because of the nature of its infections. Although the hepatocytes are the principal site of viral infection, pathological features of HBV infection have been identified in extrahepatic tissues such as the kidneys, lymph nodes, spleen, gonads, thyroid gland, adrenal glands, and bone marrow [Hollinger, 1996; Hilleman, 2003]. The liver plays an essential role in protein, carbohydrate, and lipid metabolism, energy storage and conversion, blood homeostasis, chemical detoxification, and immunity to microbial infections [Seeger and Mason, 2000]. Disruption of this organ by HBV infection therefore leads to a varying array of acute and chronic disease manifestations. 3

15 The consequences of acute HBV infection are highly variable, ranging from subclinical and asymptomatic to clinically apparent disease [Robinson, 1994]. The incubation period of hepatitis B the time from infection to the onset of signs or symptoms ranges from six weeks to six months, with the development of clinical symptoms being highly dependent on the age of the host [Mahoney, 1999]. Clinical manifestations do not generally occur in neonates, while infection produces typical illness in only 5 to 15% of children aged one to five years [McMahon et al., 1985; Mahoney, 1999]. In contrast, 33 to 50% of older children and adults develop symptomatic infections, varying in severity from mild to fulminant hepatitis with extensive liver necrosis (Figure 1.1) [Mahoney, 1999]. The clinical signs and symptoms of acute HBV infection that result from hepatic inflammation, include fever, jaundice, malaise, nausea, vomiting, abdominal pain, and increased serum levels of the liver enzymes aspartate aminotransferase (AST) and alanine aminotransferase (ALT) [Francois et al., 2001]. Fulminant hepatitis, appearing suddenly, rapidly, and with great intensity, occurs in 1 to 2% of acute infections and has a case-fatality ratio of 63 to 93% [Mahoney, 1999]. The risk of developing chronic HBV infection defined as the presence of HBsAg in the serum for longer than six months decreases with age: approximately 90% of infected neonates, 50% of infants, 30% of children, and 10% of infected adults become HBV carriers [Hilleman, 2003]. Individuals with chronic hepatitis B infections generally have one of three types of disease chronic persistent hepatitis, chronic active hepatitis, or cirrhosis [Mahoney, 1999]. The degree of histological injury is often not reflected by the symptoms, such that persons with severe chronic liver disease may remain asymptomatic until late in the course of their illness [Mahoney, 1999]. Chronic active hepatitis leads to the development of liver fibrosis and often to cirrhosis, an irreversible condition in which 4

16 100% Transient Subclinical Infection 55% Resolution Resolution Inactive Cirrhosis Resolution Recovery Acute HBV Infection 35% 10% Chronic Infection 10-30% Chronic Hepatitis Cirrhosis Dysplasia HCC Death 99% Acute Hepatitis 1% 70-90% Asymptomatic Chronic Carrier 7-37% Fulminant Hepatitis 63-93% Death Figure 1.1 Schematic representation of the pathogenesis of hepatitis B virus infection in adults, indicating the percentage of infections that progress to various forms of the disease [Modified from Feitelson, 1994]. 5

17 regenerative nodules and fibrosis cause severe liver injury [Mahoney, 1999; Ganem and Prince, 2004]. Because of its stimulating effect on hepatocyte regeneration, cirrhosis may subsequently lead to the development of hepatocellular carcinoma (HCC), a malignant liver tumour that typically appears 25 to 30 years after the onset of infection [Mahoney, 1999] and culminates in the death of the individual (Figure 1.1). The pathogenesis of hepatitis B is extremely complex [Hilleman, 2003]. Although HBV causes hepatitis B, the virus itself is not directly cytopathic in humans and therefore causes only limited damage to the liver [Francois et al., 2001]. The clinical effects of the disease are, instead, the result of the destruction of infected hepatocytes by the host immune defence system [Hollinger, 1996]. Variations in the clinical outcome of HBV infection are therefore caused by differences in the host response and, possibly, by mutations in the HBV genome that result in the production of variant viruses [Feitelson, 1994; Kidd- Ljunggren, 1996]. Although the mechanism of liver injury in acute and chronic hepatitis B is not completely defined [Robinson, 1994], it is known that aggressive immune responses, involving both major histocompatibility complex (MHC) class II-restricted, CD4+ helper cells and MHC class I-restricted, CD8+ cytotoxic T-lymphocytes [Ganem and Prince, 2004], result in symptomatic acute hepatitis and viral clearance, while non-aggressive host responses that reflect weak T-cell-mediated immune responses lead to an asymptomatic chronic viral carrier state [Hilleman, 2003]. Of the approximately 387 million chronic carriers of HBV worldwide, 15-40% eventually develop cirrhosis, liver failure, or HCC [Lok, 2002]. In addition, HBV infection results in 6

18 to 1.2 million deaths each year, making it the tenth leading cause of death worldwide, while HCC is the fifth most common cancer, killing to people per year [Lavanchy, 2004] Epidemiology Present mainly in blood, saliva, and semen, hepatitis B virus is transmitted horizontally by percutaneous or permucosal exposure to infectious blood and body fluids, or perinatally from an infected mother to her infant during the perinatal period [Mahoney, 1999; Alter, 2003]. As a highly resilient virus, HBV is resistant to breakdown and can therefore also survive outside the body for longer than a week [Alter, 2003; Lavanchy, 2004]. The prevalence of HBV infection and patterns of transmission vary greatly in different geographic regions of the world and in different population subgroups (Figure 1.2) [Mahoney, 1999; Lavanchy, 2004]. Approximately 45% of the global population live in areas where the prevalence of chronic HBV infection is high (8% or more of the population is HBsAg positive), 43% live in areas with moderate prevalence (2 to 7% of the population is HBsAg positive), and 12% live in areas of low endemicity (less than 2% of the population is HBsAg positive) [Mahoney, 1999]. 7

19 Figure 1.2 World map showing geographic distribution of chronic HBV infection [Strauss and Strauss, 2002]. In areas of high endemicity including sub-saharan Africa, most of Asia and the Middle East, the Amazon Basin of South America, the Pacific Islands, and other special population groups such as Native Alaskans, Australian Aborigines, and Maoris in New Zealand the most common source of infection is through perinatal transmission or through infection acquired horizontally during early childhood [Mahoney, 1999; de Franchis et al., 2003]. The high proportion of infectious HBV carriers explains the high rate of perinatal and childhood transmission, which perpetuate the high prevalence of HBV infections in these endemic countries [de Franchis et al., 2003]. Thus, the lifetime risk of HBV infection in such highly endemic areas is greater than 60% [Mahoney, 1999]. In areas of moderate endemicity, such as North Africa, some of the Middle East, the southern parts of Eastern and Central Europe, the USSR, the Indian subcontinent, and part of Brazil, the current important modes of HBV transmission are needle sharing among 8

20 injecting drug users, nosocomial (hospital) transmission, tattooing, and body piercing [de Franchis et al., 2003]. In contrast to highly endemic countries, the lifetime risk of HBV infection in intermediate areas is 20 to 60% [Mahoney, 1999], with over 95% of new infections being acquired during adulthood [de Franchis et al., 2003]. Areas of low HBV endemicity include Northwest Europe, Australia, and North America [Mahoney, 1999; de Franchis et al., 2003]. In these regions, most HBV infections are acquired by horizontal transmission in early adulthood: through needle sharing among injecting drug users and through sexual contacts [de Franchis et al., 2003; Lavanchy, 2004]. Other rare sources of infection include contaminated surgical instruments, needlestick injuries by hospital personnel, and blood transfusions [Alter, 2003]. The lifetime risk of infection in these developed countries is less than 20%, with most infections occurring amongst well-defined risk groups [Mahoney, 1999]. In South Africa, a country with intermediate HBV endemicity and pockets of high endemicity [Dusheiko et al., 1989a; Dusheiko et al., 1989b], more than 70% of the population has been exposed to HBV and approximately four million (almost entirely black people) are carriers [Kew, 1996; Tsebe et al., 2001]. Of these, an estimated to people die per annum [Mphahlele et al., 2002]. The majority of black carriers of HBV are infected in early childhood by horizontal transmission, probably by infected blood or saliva through skin abrasions, lesions, and bites, and tribal scarification or tattooing with unsterilised sharp instruments [Kew, 1996; Kiire, 1996]. Their main sources of infection are other family members, such as highly infectious siblings aged between one and five years, and playmates of the same age [Kew, 1996]. In contrast to it being the major source of HBV infection in Southeast Asia, maternal-infant perinatal infection is 9

21 relatively uncommon in black Africans [Kew, 1996]. The carrier rate of HBV differs regionally in South Africa, with higher rates of infection in rural areas (5 to 15%) than in urban areas (less than 5%) [Dusheiko et al., 1989a; Dusheiko et al., 1989b]; however, this difference cannot be explained by socioeconomic inequalities [Mphahlele et al., 2002] Classification The hepatitis B virus (HBV) was the first member to be discovered within the family of viruses designated the Hepadnaviridae (hepatotropic DNA viruses) [van Regenmortel et al., 2000]. This family was subsequently divided into two groups, the orthohepadnaviruses (mammalian hepadnaviruses), of which HBV is the prototype member, and the avihepadnaviruses (avian hepadnaviruses) [van Regenmortel et al., 2000]. Hepadnaviruses share many epidemiologic and biological features. As their names imply, all hepadnaviruses are hepatotropic and can cause hepatitis in their native host, and all exhibit a narrow host range that may be determined by the identity of the host hepatocyte receptor [Strauss and Strauss, 2002]. However, in contrast to orthohepadnaviruses, which mostly exhibit horizontal transmission, avihepadnaviruses are transmitted vertically [Strauss and Strauss, 2002]. 10

22 1.1.5 Virion Structure Each infectious HBV virion, or Dane particle, measuring 42 nm in diameter, consists of a spherical outer envelope that is 7 nm thick and encloses a nm electron-dense, icosahedral core particle containing the viral nucleic acid and DNA polymerase (Figure 1.3) [Hollinger, 1996]. The envelope is composed of host-derived lipids, in which three types of different sized viral surface glycoproteins are embedded [Seeger, 1994]. In the blood of HBV-infected patients, titres of Dane particles can range from less than 10 4 /ml to greater than 10 9 /ml [Ganem, 1996]. In addition to complete Dane particles, sera of HBV infected individuals also contain two distinct subviral particles: spherical 20 nm particles and tubular or filamentous particles of 20 nm diameter and variable length (Figure 1.3) [Hollinger, 1996]. Both such particles are composed exclusively of viral surface glycoproteins (~70%) and host-derived lipids, such as phospholipids, cholesterol, and triglycerides [Ganem, 1996]. However, unlike Dane particles, subviral particles lack nucleic acid and are thus non-infectious, although they remain highly immunogenic [Ganem, 1996]. The most abundant of the three types of HBV particles, 20 nm spheres can reach titres as high as /ml, while filaments can reach titres of /ml [Ganem, 1996; Locarnini, et al., 2003]. As such, subviral particles comprise over 90% of the total HBV particles in the sera of infected individuals [Paran et al., 2003]. This excess of viral surface antigen particles is thought to adsorb neutralising antibodies, thereby helping to shield the infectious virions from host defences [Ganem, 1996]. 11